Various liquid toner electrostatic imaging systems providing single color or multicolor images, appear in the patent literature. Such systems often comprise a photoconductive surface which is electrically charged and then selectively discharged by the action of incident light so as to form a latent electrostatic image. The latent image is then developed by sequential applications of liquid toners of selectable colors to the imaging surface. Liquid toners generally comprise carrier liquid in which charged toner particles are dispersed.
In some systems using liquid toners, moving developer electrodes having electrically conductive surfaces such as metal endless belts or rollers are employed. A portion of the electrode is closely spaced from the imaging surface so as to form a development region therewith to enhance the electrostatic field at the imaging surface and transport excess carrier liquid and toner particles out of the development region.
U.S Pat. No. 4,400,079 to Landa describes a developing system utilizing a roller electrode having a conductive outer surface, a portion of which is closely spaced from the imaging surface. The roller is at least partly immersed in a pool of liquid developer. In one embodiment of the invention, the hydrodynamic force of the layer of developing liquid formed on the roller is utilized to space the roller the required distance from the imaging surface. In another embodiment, mechanical spacing means, such as a pair of spacing rollers, is used to maintain the spacing of the roller from the imaging surface. The patent also indicates the possibility of providing a thin insulating layer on the conductive surface of the developing roller electrode to avoid intimate electrical contact with the background regions of the image areas, apparently useful when no mechanical spacing means is provided. A foam wiper pad mounted against the surface of the electrode is used to remove toner deposits therefrom.
In some systems employing metallic developer electrode surfaces, used toner particles adhering to the developer electrode are removed therefrom downstream of the development region by one or more resilient blades which engage the cylindrical surface of the developer roller. U.S. Pat. No. 4,454,833 has a single doctor blade made of flexible material such as urethane or Mylar, mounted against a portion of an applicator roll which is partly submerged in liquid developer. U.S. Pat. No. 3,910,231 describes a system for removing used toner from a drum or belt including blades secured to rotatable shafts and disposed for operation in response to each color.